The standard is frosted glass although there are fresnel replacements available. Does help brighten up the image. I saw some fresnel 4x5 glass on E-B*y just yesterday._________________Cro-Magnon preferred Digital.

Probably not. If I recall, the resident historian that no longer posts here except for rare occasion correctly, the Ektalite Field Lens was introduced about a year after the Graflok back.
In the service manual http://www.graflex.org/manuals/45-Pacemaker-Speed-and-Crown-Graphic.pdf pdf page 12, manual page 6 paragraph D lists the part numbers for the Ektalite Field Lens and the amount to mill off the bosses on all 3 types of backs in use on Graflex Corp. cameras._________________The best camera ever made is the one that YOU enjoy using and produces the image quality that satifies YOU.

There's two different variations of the casting for the Pacemaker backs confusingly they are the same casting number.

Essentially the original backs had a plain ground glass screen, later they were available with the Kodak Ektalite fresnel This was an otion father than the norm for some time) however the posts that the GG screen sits on differ and are shorter to allow the fresnel which fits in front (lens side) of the GG screen.

If you put two focus frames side by side one designed for the other without the difference is apparent.

If the focus frame is not designed for a fresnel than you can fit one on the rear (outside) you need to shim the clips that hold the Glass/Fresnel in the frame if you want to use a focus hood, a bit of card strip does the job. My Crown is set up like this, with no shims the focus hood won't lock in place securely.

Adding a fresnel makes a huge difference to the brightness and ease of use. I use Pacemakers hand-held composing & focusing with the screen, a rangefinders useless as I use tilt and various lenses.

I don't think I've ever seen a Graphic back with an Ektalite panel installed, though Graflex did have service instructions for retrofitting one, it's theoretically possible. I have seen quite a few Grafloks with just the ground glass, though later ones pretty much all had the fresnel.

Adding one in front of the ground glass (as it would have been from the factory) requires milling the "feet" they sit on down by the thickness of the Ektalite panel. Any decent machine shop could probably do it, but it might be cheaper just to buy another back.